BOSTON — Isaiah Thomas clearly remembers the state of the Boston Celtics when he was acquired in a trade on Feb. 19, 2015.

They had a 20-31 record after winning just 25 games the previous season and were a long way from the upper echelon of the Eastern Conference.

Two-plus years later, the Celtics will begin the NBA playoffs this weekend as the top seed in the conference.

“They definitely wasn’t thinking No. 1 seed when I got here,” said Thomas, who came to the Celtics from the Phoenix Suns on the trade deadline day. “I know that for a fact. They were barely thinking playoffs.

“How fast it’s come says a lot about the direction this organization is going in, and the work we put in as players and coaches.”

All of that work paid off in the form of a 53-29 record that put the Celtics atop the East, two games ahead of the Cleveland Cavaliers.

They will face old friend Rajon Rondo and the Chicago Bulls in the opening round of the playoffs, with Game 1 at 6:30 p.m. Sunday at the TD Garden and Game 2 on Tuesday night.

The Celtics clinched the No. 1 seed Wednesday night when the Cavaliers, who waved the white flag this week by resting LeBron James and others, lost to the Toronto Raptors.

A few minutes later, the Celtics defeated the short-handed Milwaukee Bucks 112-94 with a strong fourth quarter to finish the regular season.

For the first time since the 2008 championship season – and only the second time since the retirement of Larry Bird – the Celtics are No. 1 in the East going into the postseason.

“I think it’s very special,” said Al Horford. “I feel like we’ve been a consistent group for most of the year. I don’t think a lot of people expected us to be in this position.”

Said Thomas: “It’s very special to me. I’ve never been a No. 1 seed, so it’s definitely something I’m excited about. But the playoff seeding goes out the window.”

The Celtics recorded the fewest wins by a top seed in a non-lockout season since the Detroit Pistons also won 53 games in 2006-07.

They dealt with injuries and illnesses that limited the regular starting lineup to just 36 games, but never lost more than three straight games and improved by five wins over a year ago.

MAGIC: Orlando fired General Manager Rob Hennigan, saying it was time to go in a different direction after missing the postseason for five straight seasons.

GRIZZLIES: Guard Tony Allen is out indefinitely with a strained calf muscle in his right leg as his team gets ready for its Western Conference playoff series with the San Antonio Spurs.